On engine oil marked 5w-30, why is the latter number higher than the first. According to engine oil manufacturers sources, the numbers indicate viscosity. 5W indicates a cold engine (winter) and 30 at normal operating temperature. But the viscosity of oil drops when heated, so why is it a higher number?
In: Engineering
They’re two different scales. A theoretical 20w-20 oil wouldn’t mean it’s the same viscosity when it is cold as when it’s hot. Within the same grouping lower numbers are more viscous so 5w oil is thinner when cold than 10w is.
I’m not really sure why they use different numbers. My guess would be using the same scale for cold and hot would result in a huge gap in the middle
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